1. Field of the Invention
The present invention relates to a hydrogen gas supply device for hydrogen engines.
2. Description of Related Art
The development of the hydrogen engine as a form of non-polluting engine system has been progressing in recent years. In order to supply hydrogen fuel to this type of engine, metal hydrides (which are hereafter referred to as metal hydride alloys), contained in tanks (which are hereafter referred to as metal hydride alloy tanks) which are mounted on vehicles, have been employed to occlude or storage and release hydrogen. Such hydrogen engine configurations or systems are known from, for example, Japanese Unexamined Patent Publications Nos. 62-279264 and 63-246458.
However, to effect release of occluded hydrogen in metal hydride alloy tanks at a specific predetermined pressure, i.e. the optimal release pressure, 4-10 atm., for example, for injection into the hydrogen engine, the metal hydride-alloy tanks must be maintained at a temperature corresponding to the optimal release pressure. To this end, in the hydrogen engine system described in Japanese Unexamined Patent Publication No. 63-246458, hot water is produced by heat exchange with exhaust gas from the hydrogen engine and circulated through the metal hydride alloy tanks as a heat medium.
On the other hand, coolant is conventionally circulated through an engine cylinder block to prevent the engine from being overheated. The coolant is generally heated to temperatures exceeding 90.degree. C. in the course of this circulation. Accordingly, a configuration in which coolant is circulated as a heat medium through the metal hydride alloy tank permits a simpler overall design than the abovementioned configuration in which hot water is generated by the aid of exhaust gas.
In a system in which engine coolant is circulated through the metal hydride alloy tank as a heat medium, a metal hydride tank, which contains a metal hydride alloy which releases hydrogen at the optimal release pressure in the temperature range of, for example, 60.degree.-90.degree. C., is mounted on a vehicle.
During engine startup, even when coolant water of approximately the same temperature as ordinary temperature of atmospheric or ambient air, i.e, between 15.degree. C. and 25.degree. C., is circulated, release of hydrogen at the optimal release pressure is not achieved with the metal hydride alloy tank. Thus, an extra metal hydride alloy tank, which in turn is used for startup, has conventionally been mounted on the vehicle. That is, this extra metal hydride alloy tank (which is hereafter referred to as a startup tank for simplicity) contains a metal hydride alloy having temperature-pressure properties making it possible to achieve optimal release pressure at an ambient air temperature of approximately 10.degree. C. The hydrogen engine is started with hydrogen generated in the startup metal hydride alloy tank. When the coolant exceeds, for example, approximately 60.degree. C. due to subsequent warming, the supply of hydrogen to the hydrogen engine is switched over from the startup hydride alloy tank to the metal hydride alloy tank (which is hereafter referred to as the mobile tank for simplicity). After a wait to allow engine operation to stabilize after the switchover of tanks, vehicle drive is initiated.
However, in vehicles equipped with two types of metal hydride-alloy tanks for startup and running as described above, since the temperature of the coolant is raised by warming after hydrogen engine startup and the vehicle does not run until the switchover of tanks has been made to the mobile tank from the startup tank, starting reliability decreases. Moreover, hydrogen released by the startup tank during warming is not applied to running, lowering fuel efficiency with respect to actual mileage.
Although the startup metal hydride alloy described above could conceivably be stored in high-pressure containers capable of withstanding pressures of approximately 10 atm. and above, and hydrogen from these containers could be supplied to the hydrogen engine during running as well, drawbacks are encountered when mounting such high-pressure containers in vehicles in the form of various additional elements required to ensure safety, thus complicating the configuration and precluding weight reduction.